XML SCHEMA BASED AOP WITH SPRING

Transcription

1 XML SCHEMA BASED AOP WITH SPRING Copyright tutorialspoint.com To use the aop namespace tags described in this section, you need to import the spring-aop schema as described below: <?xml version="1.0" encoding="utf-8"?> <beans xmlns=" xmlns:xsi=" xmlns:aop=" xsi:schemalocation=" "> <!-- bean definition & AOP specific configuration --> </beans> You will also need following AspectJ libraries on the CLASSPATH of your application. These libraries are available in the 'lib' directory of an AspectJ installation, otherwise you can download them from the internet. aspectjrt.jar aspectjweaver.jar aspectj.jar aopalliance.jar Declaring an aspect An aspect is declared using the <aop:aspect> element, and the backing bean is referenced using the ref attribute as follows: Here "abean" will be configured and dependency injected just like any other Spring bean as you have seen in previous chapters. Declaring a pointcut A pointcut helps in determining the join points iemethods of interest to be executed with different advices. While working with XML Schema based configuration, pointcut will be defined as follows: expression="execution(* com.xyz.myapp.service.*.*(..))"/>

2 The following example defines a pointcut named 'businessservice' that will match the execution of getname method available in Student class under the package com.tutorialspoint: expression="execution(* com.tutorialspoint.student.getname(..))"/> Declaring advices You can declare any of the five advices inside an <aop:aspect> using the <aop:{advice NAME> element as given below: expression="execution(* com.xyz.myapp.service.*.*(..))"/> <!-- a before advice definition --> <aop:before pointcut-ref="businessservice" <!-- an after advice definition --> <aop:after pointcut-ref="businessservice" <!-- an after-returning advice definition --> <!--The dorequiredtask method must have parameter named retval --> <aop:after-returning pointcut-ref="businessservice" returning="retval" <!-- an after-throwing advice definition --> <!--The dorequiredtask method must have parameter named ex --> <aop:after-throwing pointcut-ref="businessservice" throwing="ex" <!-- an around advice definition --> <aop:around pointcut-ref="businessservice" You can use same dorequiredtask or different methods for different advices. These methods will be defined as a part of aspect module. XML Schema Based AOP Example To understand above mentioned concepts related to XML Schema Based AOP, let us write an example which will implement few of the advices. To write our example with few advices, let us

3 have working Eclipse IDE in place and follow the following steps to create a Spring application: Step Description 1 Create a project with a name SpringExample and create a package com.tutorialspoint under the src folder in the created project. 2 Add required Spring libraries using Add External JARs option as explained in the Spring Hello World Example chapter. 3 Add Spring AOP specific libraries aspectjrt.jar, aspectjweaver.jar and aspectj.jar in the project. 4 Create Java classes Logging, Student and MainApp under the com.tutorialspoint package. 5 Create Beans configuration file Beans.xml under the src folder. 6 The final step is to create the content of all the Java files and Bean Configuration file and run the application as explained below. Here is the content of Logging.java file. This is actually a sample of aspect module which defines methods to be called at various points. package com.tutorialspoint; public class Logging { * before a selected method execution. public void beforeadvice(){ System.out.println(""); * after a selected method execution. public void afteradvice(){ System.out.println(""); * when any method returns. public void afterreturningadvice(object retval){ System.out.println("Returning:" + retval.tostring() ); * if there is an exception raised. public void AfterThrowingAdvice(IllegalArgumentException ex){ System.out.println("There has been an exception: " + ex.tostring()); Following is the content of the Student.java file: package com.tutorialspoint;

4 public class Student { private Integer age; private String name; public void setage(integer age) { this.age = age; public Integer getage() { System.out.println("Age : " + age ); return age; public void setname(string name) { this.name = name; public String getname() { System.out.println("Name : " + name ); return name; public void printthrowexception(){ System.out.println("Exception raised"); throw new IllegalArgumentException(); Following is the content of the MainApp.java file: package com.tutorialspoint; import org.springframework.context.applicationcontext; import org.springframework.context.support.classpathxmlapplicationcontext; public class MainApp { public static void main(string[] args) { ApplicationContext context = new ClassPathXmlApplicationContext("Beans.xml"); Student student = (Student) context.getbean("student"); student.getname(); student.getage(); student.printthrowexception(); Following is the configuration file Beans.xml: <?xml version="1.0" encoding="utf-8"?> <beans xmlns=" xmlns:xsi=" xmlns:aop=" xsi:schemalocation=" "> expression="execution(* com.tutorialspoint.*.*(..))"/> <aop:before pointcut-ref="selectall" method="beforeadvice"/> <aop:after pointcut-ref="selectall" method="afteradvice"/> <aop:after-returning pointcut-ref="selectall" returning="retval" method="afterreturningadvice"/>

5 <aop:after-throwing pointcut-ref="selectall" throwing="ex" method="afterthrowingadvice"/> <!-- Definition for student bean --> <property name="name" value="zara" /> <property name="age" value="11"/> <!-- Definition for logging aspect --> <bean /> </beans> Once you are done with creating source and bean configuration files, let us run the application. If everything is fine with your application, this will print the following message: Name : Zara Returning:Zara Age : 11 Returning:11 Exception raised There has been an exception: java.lang.illegalargumentexception.. other exception content Let me explain that above defined > selects all the methods defined under the package com.tutorialspoint. Let us suppose, you want to execute your advice before or after a particular method, you can define your pointcut to narrow down your execution by replacing stars in pointcut definition with actual class and method names. Below is a modified XML configuration file to show the concept: <?xml version="1.0" encoding="utf-8"?> <beans xmlns=" xmlns:xsi=" xmlns:aop=" xsi:schemalocation=" "> expression="execution(* com.tutorialspoint.student.getname(..))"/> <aop:before pointcut-ref="selectall" method="beforeadvice"/> <aop:after pointcut-ref="selectall" method="afteradvice"/> <!-- Definition for student bean --> <property name="name" value="zara" /> <property name="age" value="11"/> <!-- Definition for logging aspect --> <bean />

6 </beans> If you will execute sample application with these configuration changes, this will print the following message: Name : Zara Age : 11 Exception raised.. other exception content Loading [MathJax]/jax/output/HTML-CSS/jax.js